Approximately half the world's population uses biomass fuels for domestic energy, resulting in widespread exposure to indoor air pollution (lAP). Indicators of lAP have been associated with acute respiratory infections, obstructive airway disease, adverse pregnancy outcomes, and cancer. More than 2 million deaths are attributed to lAP each year. Still, few studies have directly examined the association between pollutants in biomass smoke and human health. Furthermore, there have been no intervention studies to assess the effectiveness of preventive measures in decreasing lAP and respiratory disease. We propose to address these deficiencies through detailed epidemiological studies in Santa Ana, Ecuador. Preliminary studies have shown a high prevalence of respiratory infection in the community, with approximately 50% of homes using biomass fuel. Proposed investigations will examine the effectiveness of improved biomass stoves and ventilation to decrease lAP in an ideal (laboratory) setting as well as in rural houses in Santa Ana. We will also assess the association of respiratory disease and lAP levels among 60 households in the community. Lastly, we will test the effectiveness of preventive measures to decrease the incidence of acute lower respiratory infections, using a randomized, controlled, study design. Through these investigations we hope to provide insight into an environmental hazard that is widespread throughout the world.